In recent years, it has been sought after that wafers become larger, and, as the wafers become larger, in slicing of an ingot a wire saw apparatus is primarily used.
The wire saw apparatus is an apparatus for slicing out a large number of wafers at the same time by making a wire (high-tensile steel wire) travel at high speed and pressing an ingot (work) against the wire to slice the ingot while spraying slurry on the wire (Japanese Unexamined Patent Publication (Kokai) No. 9-262826).
Here, in FIG. 12, an outline of an example of a common wire saw apparatus is shown.
As shown in an overall view of FIG. 12(A), a wire saw apparatus 101 mainly includes a wire 102 for slicing an ingot, grooved rollers 103 (wire guides) around which the wire 102 is wound, a mechanism 104 for providing the wire 102 with tension, a mechanism 105 for feeding the ingot to be sliced, and a mechanism 106 for supplying slurry at the time of slicing.
The wire 102 is unreeled from one wire reel 107, and enters the grooved rollers 103 via a traverser 108 through the tension-providing mechanism 104 including a powder clutch (constant torque motor 109), a dancer roller (deadweight)(not shown), etc. After the wire 102 is wound around the grooved rollers 103 about 300 to 400 times, it is reeled onto a wire reel 107′ through the other tension-providing mechanism 104′.
Moreover, the grooved roller 103 is a roller formed as a steel cylinder around which polyurethane resin (a shell unit) is press-fitted, the roller having grooves cut on the surface thereof at a predetermined pitch, and is configured such that the wire 102 wound around the roller can be driven in the reciprocating direction by a motor 110 for driving in a predetermined cycle.
Here, the grooved roller 103 will be further explained. A grooved roller shown in FIG. 13 is taken up as an example of the conventionally used grooved roller 103. At both ends of the grooved roller 103, bearings 121 and 121′ supporting a shaft 120 of the grooved roller are provided. For example, the bearing 121 is of the radial type, and the grooved roller 103 can extend in an axial direction toward the bearing 121 of the radial type. On the other hand, the bearing 121′ is of the thrust type, and the grooved roller 103 is configured so as not to extend toward the bearing 121′ of the thrust type easily. That is, the grooved roller is configured such that it can extend in only one direction entirely, in the axial direction.
Moreover, some grooved rollers are configured such that both the bearings 121 and 121′ are of the radial type, and the grooved roller can extend back and forth in an axial direction.
When an ingot is sliced, the ingot is fed to the wire 102 wound around the grooved rollers 103 by the ingot-feed mechanism 105 as shown in FIG. 12(B). This ingot-feed mechanism 105 includes an ingot-feed table 111 for feeding an ingot, an LM guide 112, an ingot clamp 113 for holding the ingot, a slice pad plate 114, and the like, and can feed the ingot fastened to the end thereof at a previously programmed feed speed by driving the ingot-feed table 111 along the LM guide 112 by computer control.
And, as shown in FIG. 12(A), nozzles 115 are provided near the grooved rollers 103 and the wound wire 102, whereby it is possible to supply slurry which is a liquid in which GC (silicon carbide) abrasive grains, for example, are dispersed to the grooved rollers 103 and the wire 102 from a slurry tank 116 at the time of slicing. In addition, a slurry chiller 117 is connected to the slurry tank 116, making it possible to adjust the temperature of the slurry to be supplied.
An ingot is sliced by using such a wire saw apparatus 101 and applying appropriate tension to the wire 102 by using the wire-tension-providing mechanism 104, while making the wire 102 travel in the reciprocating direction with the motor 110 for driving.
Currently, it is common to perform slicing by using a wire having a width of 0.13 mm to 0.18 mm, applying a tension of 2.5 kgf to 3.0 kgf thereto, and making the wire travel in the reciprocating direction at an average speed of 400 m/min to 600 m/min in a cycle of 1 c/min to 2 c/min (30 s/c to 60 s/c).